Portable back rest



FIG. 1 is a perspective view of the portable back rest embodying the design of the present invention;

FIG. 2 is a front elevational view thereof, the rear being a mirror image of the front shown in FIG. 2;

FIG. 3 is an end elevational view thereof;

FIG. 4 is an end elevational view thereof;

FIG. 5 is a top plan view thereof; and,

FIG. 6 is a bottom view thereof. 

The ornamental design for a portable back rest, as shown and described. 